1. Field of Invention
This invention is directed to tensioning wires and retaining tensioned wires.
2. Description of Related Art
FIG. 1 illustrates one conventional apparatus and technique for tensioning wires and retaining such tensioned wires under tension. As shown in FIG. 1, the current process and apparatus for tensioning wires and retaining the tensioned wires under tension requires each wire 110 to be formed with looped ends 112. As shown in FIG. 1, a wire tension module 100 includes a pair of tensioning portions 120 and 130. End members 124 and 134 of the tensioning portions 120 and 130, respectively, are rigidly mounted and spaced apart on a substrate member 140. Tension blocks 122 and 132 of the tensioning portions 120 and 130, respectively, are slidably placed on the substrate member 140 and attached by screws 128 and 138 to the end members 124 and 134, respectively. Each of the tensioning blocks 122 and 132 includes a post 126 and 136, respectively. The wire to be tensioned 110 is connected between the tension blocks 122 and 132 by placing one of the looped ends 112 over each of the posts 126 and 136.
A tensile force is then placed on the wire to be tensioned 110 by turning one or both of the screws 128 and 138 in a direction that draws the respective blocks 122 and 132 towards the corresponding end members 124 or 134. That is, the screws 128 and/or 138 are turned to move the blocks 122 and 132 away from each other. The tension and, more importantly, the vibrational frequency, in the wire free span is thus set by pulling on one or more of the blocks 122 and/or 132 using the respective screws 128 and 138 to elongate the wire 110.
As shown in FIG. 1, the screws 128 and 138 pass through passages 125 and 135 in the end members 124 and 134, respectively, and engage with threaded passages 123 and 133 formed in the blocks 122 and 132, respectively. It should be appreciated that, based on the amount of elongation of the wire 110 required to obtain the desired tension or vibrational frequency in the wire free span, both end portions 120 and 130 may be required. Alternatively, if only a relatively small of elongation is required to obtain the desired or vibrational frequency, one of the end portions 120 or 130 can be replaced with a post 126 or 136 that is rigidly fixed to an expanded end member 124 or 134.
However, the inventors of the invention described herein have determined that this process is very difficult to automate and requires an excessively large number of parts in the wire module 100. These two factors lead to a significantly high manufacturing cost for the wire module 100.
This invention provides systems and methods for tensioning wires to be tensioned that moves the tensioning function from the wire module to an apparatus external to the wire module.
This invention separately provides systems and methods for retaining externally-tensioned wires under tension in the wire module.
However, externally tensioning and measuring the tension applied to the wires to be incorporated into the wire module is difficult. In particular, it is often difficult to accurately hold the wire in place or even to accurately handle the wire. Additionally, the wire""s own characteristics and/or sensitivities limit the ability of conventional external wire tensioning systems to accurately and repeatedly tension the wires to the desired vibrational frequency.
This invention provides systems and methods for tensioning wires externally to the wire module.
This invention further provides systems and methods for externally tensioning the wires that allows desired tension values to be set, automatically attained, and maintained in a repeatable manner.
This invention separately provides an external tensioning device that can apply and measure tension in a very fine wire.
This invention separately provides systems and methods for applying measuring and maintaining tension using closed loop feedback.
This invention separately provides systems and methods for automatically tensioning wire that permits various tension factors and parameters to be easily set.
By removing the tensioning function from the wire module, the cost of the wire module can be reduced. In particular, shifting the tensioning function to an external wire tensioning apparatus allows the number of parts in the wire module to be reduced and allows more flexibility in automating the tensioning and tensioned wire retaining processes.
According to one exemplary embodiment of the systems and methods for retaining externally-tensioned wires according to this invention, one or more wires are tensioned using an apparatus that is external to the wire module. The one or more externally-tensioned wires to be incorporated into the wire module are then placed, at each end of the wire module, between a first, fixed member and a second, detachable member. Each of the detachable members is detachably attached to the corresponding fixed member. In particular, a force normal to the tension direction in the one or more wires is generated between the detachable and fixed members to clamp or otherwise securely hold the externally tensioned wires at each end of the wire module. This retains the externally applied tension in the wires between the end portions of the wire module. The distance between the end portions of the wire module and the tension in the clamped tensioned wires is selected so that the desired vibrational frequency in the free wire span between the end portions of the wire module is obtained.
In one exemplary embodiment, the clamping surfaces of the first member and the second member extend parallel to the free span of the tensioned wires. In a second exemplary embodiment, the clamping surfaces of the first member and the second member are angled relative to the plane defined by the free span of the tensioned wires. In this second exemplary embodiment, the first member has a curved portion extending between the clamping surface of the first member and the plane defined by the wire free spans of the tensioned wires.
The inventors of this invention have determined that clamping the tensioned wires in this manner will hold the tensioned wires at the desired vibrational frequency. The inventors have also determined that dissimilar materials for the clamping surface improves the long term stability in holding the tensioned wires at the desired vibrational frequency. However, using dissimilar materials for the clamping surface wire is not required.
In one exemplary embodiment of the external wire tensioning systems and methods of this invention, a wire tensioning device includes a base plate. A three-axis slide system is mounted at one end of the base plate and a wire holding fixture is provided at the other end of the base plate. A feedhead assembly is mounted on the three-axis slide system. Two of the slides of the three-axis slide system are used to position the feedhead assembly perpendicular to and across the base plate. The third slide of the three-axis slide system is used to apply tension to the wire between the wire holding fixture at one end of the base plate and the feedhead assembly at the other end of the base plate.
In various exemplary embodiments, the feedhead assembly includes a load cell used to measure the tension applied to the wire between the feedhead assembly and the wire holding fixture. A servo control system inputs a signal from the load cell and applies a drive signal to the third slide of the three-axis slide system based on the difference between a desired wire tension value and the wire tension measured by the load cell. Thus, the load cell servo control system and third slide of the three-axis slide system use closed-loop feedback control.
In one exemplary embodiment of the feedhead assembly including the load cell, the wire to be tensioned is stored on a wire spool. The wire is drawn from the wire spool through a pivot arm and connected to the wire holding fixture at the other end of the base plate. The wire spool is then secured to prevent any additional wire from being withdrawn from the wire spool. When the third slide of the three-axis slide system is driven to a apply tension to the withdrawn portion of the wire, the tension applied to the wire causes the pivot arm to pivot against the load cell. The force of the pivot arm against the load cell generates a load cell signal that is provided to the servo control system.
The servo control system compares the value of the signal from the load cell to a desired load cell value representative of the desired tension to be applied to the withdrawn portion of the wire. When the value of the load cell signal is less than the desired value, the servo control system drives the third slide of the three-axis slide system to move the feedhead assembly away from the wire holding fixture to apply additional tension to the withdrawn portion of the wire. In contrast, when the value of the signal from the load cell is greater than the desired value, the servo control system drives the third slide of the three-axis slide system to move the feedhead assembly closer to the wire holding fixture to reduce the tension on the withdrawn portion of the wire.
In various other exemplary embodiments, rather than placing a load cell in the feedhead assembly to measure the tension in the wire, the vibrational frequency of the wire is measure. In many uses of such tensioned wires, the vibrational frequency, rather than the wire tension, is the critical parameter. Thus, the tension is used only as a proxy for the vibrational frequency.
In various exemplary embodiments, the vibrational frequency is measured electronically, using capacative or inductive sensors. Alternatively, in various other exemplary embodiments, the vibrational frequency is measured mechanically. Regardless of how the vibrational frequency is measured, a servo control system inputs a signal from the vibrational frequency sensor and applies a drive signal to the external-tension applying system, such as the three axis slide system, until the measured vibrational frequency is equal to the desired vibrational frequency. Thus, the servo control system, the external tension applying system and the vibrational frequency sensor form a closed-loop feedback control system.
In various exemplary embodiments, the third slide of the three-axis slide system moves in a direction parallel to the withdrawn portion of the wire. In a second exemplary embodiment, the withdrawn wire is partially wrapped around a first post so that the third slide moves in a direction that is at an angle to the portion of the wire extending between the first post and the wire holding fixture. In a third exemplary embodiment, the wire holding fixture includes a second post. In this case, the wire from the feedhead assembly, whether coming directly from the feedhead assembly or coming from the feedhead assembly after being wrapped around the first post, is wrapped around the second post before being held by the wire holding fixture.
In various exemplary embodiments that combine the external wire tensioning apparatus and the wire module according to this invention, the first and second posts can comprise curved portions of the first members positioned at each end of the wire module.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of various exemplary embodiments of the systems and methods according to this invention.